hush: fix expansion of quoted $VAR, $* and $@

diff --git a/shell/hush_test/hush-parsing/quote4.tests b/shell/hush_test/hush-parsing/quote4.tests
new file mode 100755
index 0000000..f1dabfa
--- /dev/null
+++ b/shell/hush_test/hush-parsing/quote4.tests
@@ -0,0 +1,2 @@
+a_b='a b'
+echo "$a_b"